The present invention relates to a resist composition excellent in flame resistance for permanent protective coating of a printed wiring board. More specifically, it relates to a resist composition for permanent protective coating of a printed wiring board which resist composition contains almost no halogen, almost no phosphorus and almost no antimony and is excellent in flame resistance. A printed wiring board obtained by applying the resist composition of the present invention, drying the applied resist composition and curing the dried resist composition is suited mainly for use in a semiconductor plastic package as a high-density and small-sized printed wiring board. The resist composition of the present invention is applied on a printed wiring board surface having copper circuits formed, a solvent is removed from the applied composition by heating as required, and then the resist composition is thermally-cured or photically-cured. Otherwise, the resist composition is selectively photically-cured, not-cured portions are developed and removed, and the resist composition is thermally post-cured. The thus-obtained coating is used as a permanent protective coating for a printed wiring board.
Conventionally, a thermosetting type resist, a photo-setting type resist and a photo-setting/thermosetting type resist used as a permanent protective coating for a printed wiring board are a resin composition having no self-extinguishing properties in itself. The above resin composition is applied to the surface of a laminate containing a bromine compound and the applied resin composition is dried and then cured. When the laminate fires, the bromine compound contained in the laminate burns and decomposes to generate a bromine gas and the bromine gas prevents the permanent protective coating as the external layer from burning. In this case, as a result, the laminate as a whole can attain V-0 (self-extinguishing properties) in the UL 94 standard. However, when the above resin composition having no self-extinguishing properties is applied to a halogen-free, phosphorus-free and antimony-free laminate containing no bromine, dried and then cured, the resultant laminate naturally has an inflammable permanent protective coating as an external layer. In this case, since water and a gas which generate when the laminate burns do not prevent so much the permanent protective coating as an external layer from burning, the laminate as a whole shows inflammability. Further, attempts have been made to impart flame retardancy to a permanent protective coating itself as an external layer. As a method for improving the flame resistance of a laminate as a whole by increasing the flame resistance of a flame-retardant permanent protective coating itself, it is necessarily required to incorporate halogen, phosphorus, antimony, etc., into a coating agent for the above permanent protective coating. However, the coating agent containing halogen, phosphorus, antimony, etc., has problems. Therefore, developments of a coating agent which does not contain the above compounds are expected. For this reason, there has not been produced a printed wiring board comprising a halogen-free, phosphorus-free and antimony-free permanent protective coating having self-extinguishing properties (UL flame resistance V-0).
Further, a resist generally contains a color pigment. In most cases, the color pigment is green. The green pigment is generally phthalocyanine green. The molecule of the phthalocyanine green has chlorine in a large amount. Therefore, the phthalocyanine green has a problem in view of the generation of dioxin.
For imparting flame resistance and for avoiding decreasing the characteristic properties of a resist, a phosphoric compound is added in some cases. However, in order to obtain flame resistance, it is required to add a phosphoric compound in an amount of 1 to 5% by weight. Further, some additives generate a toxic substance such as phosphine during burning. Many of the resists containing a phosphoric compound have problems. Further, antimony is not preferred in view of toxicity.
As a resin for a liquid photo-setting/thermosetting coating composition which is developed with an aqueous solution containing an organic solvent or a dilute alkaline aqueous solution, there are known a resin composition (JP-A-1-139619) prepared by incorporating an aromatic epoxy compound into an unsaturated resin obtained by reacting a carboxyl-group-containing acrylate resin with a glycidyl (meth) acrylate, a resin composition (JP-A-61-243869) prepared by adding a diluent into a compound obtained by reacting a saturated or unsaturated polybasic acid anhydride with a reaction product of a novolak type epoxy resin and an unsaturated carboxylic acid, and a resin composition (JP-A-8-41150) prepared incorporating a cresol novolak type epoxy resin into a resin obtained by reacting an alicyclic epoxy-group-containing (meth)acrylate with some of carboxyl groups of a vinyl copolymer having as essential components a (meth)acrylic acid and a lactone-modified hydroxyl (meth)acrylate.
However, a resist containing the above resin composition is not a resist which itself has self-extinguishing properties (flame resistance V-0) so that imparting flame resistance has been required. In recent years, a printed wiring board is becoming denser and denser. An external-layer permanent protective coating on a high-density printed wiring board has insufficient heat resistance and anti-migration properties. Therefore, conventional resists have problems from the viewpoint of reliability also.
It is an object of the present invention to provide a resist composition for a permanent protective coating of a printed wiring board which resist composition itself has self-extinguishing properties and is excellent in flame resistance.
It is another object of the present invention to provide a halogen-free, phosphorus-free and antimony-free resist composition for a permanent protective coating of a printed wiring board which resist composition has self-extinguishing properties and is excellent in flame resistance.
It is further another object of the present invention to provide a resist composition for a permanent protective coating of a printed wiring board which resist composition is excellent in reliability such as anti-migration properties.
According to the present invention, there is provided a resist composition for permanent protective coating of a printed wiring board, which resist composition is excellent in flame resistance and is obtained by incorporating as essential components a flame retardant containing 100 to 140 parts by weight of (a) aluminum hydroxide, 0.1 to 15 parts by weight of (b) amolybdenum compound and 0.1 to 10 parts by weight of (c) a zinc stannate type compound into 100 parts by weight of a resin.
According to the present invention, further, there is provided a resist composition according to above, wherein the resin is at least one selected from the group consisting of a thermosetting resin, a photo-setting/thermosetting resin and a photo-setting resin.
According to the present invention, further, there is provided a resist composition according to above, wherein the photo-setting/thermosetting resin is a resin containing 5 to 35% by weight of (d) an epoxy resin, 20 to 90% by weight of (e) an unsaturated-group-containing polycarboxylic acid resin, 1 to 30% by weight of (f) ethylenic unsaturated monomer and 0.1 to 20% by weight of (g) a photopolymerization initiator as essential components.
According to the present invention, further, there is provided a resist composition according to above, wherein the unsaturated-group-containing polycarboxylic acid resin is a resin having an acid value of 40 to 200 mgKOH/g and obtained by reacting a reaction product of 100 parts by weight of epoxy acrylate and 5 to 40 parts by weight of a polyfunctional cyanate ester compound, with 10 to 90 parts by weight of a polybasic acid anhydride.
The resist for a permanent protective coating in the present invention includes a generally known resist. That is, there may be used any one of a thermosetting type resist, a photo-setting/thermosetting type resist and a photo-setting type resist. However, a resist containing a polyfunctional cyanate ester compound or a resist containing a resin having a molecule in which a polyfunctional cyanate ester compound is incorporated by reaction is preferably used in view of heat resistance and anti-migration properties.
The polyfunctional cyanate ester compound used in the present invention refers to a compound having a molecule containing at least 2 cyanato groups. Specific examples thereof include 1,3- or 1,4-dicyanatobenzene, 1,3,5-tricyanatobenzene, 1,3-, 1,4-, 1,6-, 1,8-, 2,6- or 2,7-dicyanatonaphthalene, 1,3,6-tricyanatonaphthalene, 4,4-dicyanatobiphenyl, bis(4-dicyanatophenyl)methane, 2,2-bis(4-cyanatophenyl)propane, 2,2-bis(3,5-dibromo-4-cyanatophenyl)propane, bis(4-cyanatophenyl)ether, bis(4-cyanatophenyl)thioether, bis(4-cyanatophenyl)sulfone, tris(4-cyanatophenyl)phosphite, tris(4-cyanatophenyl)phosphate and cyanates obtained by a reaction of novolak with cyan halide.
In addition to the above ester compounds, there may be used polyfunctional cyanate ester compounds described in Japanese Patent Publications Nos. 41-1928, 43-18468, 44-4791, 45-11712, 46-41112 and 47-26853 and JP-A-51-63149. Further, there may be also used prepolymers having a molecular weight of 400 to 6,000 and having a triazine ring formed by the trimerizing cyanato group of each of these polyfunctional cyanate ester compounds. The above prepolymer is obtained by polymerizing the above polyfunctional cyanate ester monomer in the presence of an acid such as a mineral acid or a Lewis acid; a base such as tertiary amine, e.g., sodium alcoholate, or a salt such as sodium carbonate as a catalyst. The prepolymer partially contains an unreacted monomer and is in the form of a mixture of monomer with prepolymer, and this material is preferably used in the present invention. When used, generally, the above resin is dissolved in an organic solvent in which it is soluble.
Most of resins used as a thermosetting component is an epoxy resin. This epoxy resin component (d) may be selected from generally known epoxy resins. Specifically, it includes a liquid or solid bisphenol A type epoxy resin, a bisphenol F type epoxy resin, a phenol novolak type epoxy resin, a cresol novolak type epoxy resin, an alicyclic epoxy resin; polyepoxy compounds obtained by epoxidizing the double bond of butadiene, pentadiene, vinylcyclohexene or dicyclopentyl ether; and polyglycidyl compounds obtained by reacting a polyol, a hydroxyl-group-containing silicon resin and epohalohydrin. These resins may be used alone or in combination. The epoxy resin inevitably contains chlorine. On the other hand, for the above purpose, it is preferred that the amount of chlorine is as small as possible. However, a limitation exists in view of a cost. According to the halogen-free copper-clad laminate test method, Japan Printed Circuit Association (JPCA) standard, JPCA-ES-01-1999, the amount of each of chlorine and bromine is respectively 0.09% or lower in the definition of a halogen-free material. This value is a reference as a limit value.
When the resist composition containing anyone of the above epoxy resins is thermally cured at approximately 150xc2x0 C. for approximately 1 hour, an unreacted epoxy resin remains. Accordingly, the above resist composition is poor in its adhesion to copper of a copper-circuits-possessing printed wiring board. For this reason, a potential curing agent-curing accelerator is used in order to cure the unreacted epoxy resin. The potential curing agent-curing accelerator is not specially limited. For improving a preservation stability a potential curing agent-curing accelerator having a melting point of at least 100xc2x0 C. and further having a solubility of 10% by weight in the resist composition (a solvent is included) is preferably used. The potential curing agent-curing accelerator is a curing agent which is reacted with the epoxy resin by melting, decomposition, elution, an ionic reaction or a protect cover dissolution by heating it up to at least 100xc2x0 C. and accelerates the curing of the epoxy resin. The potential curing agent curing accelerator has a small activity at a temperature lower than the melting point. The resin composition containing the potential curing agent-curing accelerator is excellent in preservation stability.
The potential curing agent-curing accelerator which is melted by heating and reacted is not specially limited. Dicyandiamide, an organic acid hydrazide, diaminomaleonitrile, melamine, derivatives of melamine, polyamine salt, and etc., can be used, while an adduct type curing agent is preferred. An amine-adduct type curing agent is further preferred. The amine-adduct type curing agent is a prepolymer type curing agent having an active hydrogen site and a catalyst-function site in a molecule and it is an adduct of an amine compound with an epoxy resin and has a melting point of at least 100xc2x0 C. Further, known potential curing agent-curing accelerator can be used. These potential curing agent-curing accelerator are dispersed as a powder, preferably a powder having a particle diameter of 5 xcexcm or less, in the resin composition. These potential curing agent-curing accelerator can be used alone or in combination. The amount of thereof is 0.1 to 10% by weight, preferably 0.2 to 8% by weight.
A heat-curing catalyst can be added in the above resist composition for further promoting curing. Although the heat-curing catalyst is not specially limited, an epoxy heat-curing catalyst having a melting point of at least 100xc2x0 C. and, more preferably, having a solubility of 10% by weight in the resist composition is added in an amount of 0.01 to 10% by weight, preferably 0.1 to 5% by weight, for maintaining a fine preservation stability. The heat-curing catalyst is uniformly dispersed as a fine powder. The imidazole type heat-curing catalyst includes 2-heptadecylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-5 hydroxymethylimidazole, 2-phenyl-4-benzyl-5-hydroxymethylimidazole and 2,4-diamino-6-{2-methylimidazolyl-(1)}-ethyl-S-triazine. The imidazole type heat-curing catalyst is limited to these. These heat-curing catalyst can be used alone or in combination.
As for the photo-setting/thermosetting type resist, the photo-setting/thermosetting resin is applied to a printed wiring board surface and then dried by heating to remove a solvent, then a photo-setting component is selectively cured by irradiation of light, an not-cured component which has not been exposed to the light is dissolved and removed with an alkaline developer, and then a thermosetting component is thermally cured by heating to give a permanent protective coating. Especially, the coating obtained from the photo-setting/thermosetting type resist containing a resin having a molecule in which a polyfunctional cyanate ester compound is incorporated by reaction, provided by the present invention, is excellent in heat resistance and there can be obtained a printed wiring board which is excellent in anti-migration properties and excellent in heat resistance as a whole.
The unsaturated-group-containing polycarboxylic acid resin as component (e) used in the photo-setting/thermosetting type resist of the present invention refers to a resin having a molecule containing a carboxyl group and an unsaturated group such as a (meth)acryloyl group. The unsaturated-group-containing polycarboxylic acid resin is selected from generally known unsaturated-group-containing polycarboxylic acid resins. Examples thereof includes generally known unsaturated-group-containing polycarboxylic acid resins such as an unsaturated-group-containing resin shown in JP-A-1-139619 and obtained by reacting a carboxyl-group-containing acrylate resin with a glycidyl (meth) acrylate, an unsaturated-group-containing resin shown in JP-A-8-41150 and obtained by reacting an alicyclic epoxy-group-containing unsaturated compound with some of carboxyl groups of a vinyl copolymer having as essential components a (meth)acrylic acid and a lactone-modified hydroxyalkyl (meth)acrylate, and a resin shown in JP-A-61-243869 and obtained by reacting a saturated or unsaturated polybasic acid anhydride with a reaction product of a novolac type epoxy resin and an unsaturated monocarboxylic acid.
Among the unsaturated-group-containing polycarboxylic acid resins as component (e) used in the present invention, preferred are an unsaturated-group-containing resin obtained by reacting an alicyclic epoxy-group-containing unsaturated compound with a carboxyl-group-containing (meth) acylate resin having as essential components a (meth) acrylic acid having an acid value of 10 to 200 mgKOH/g, a double bond of 1.0 to 3.5 mol per 1 kg of a resin and a number average molecular weight of 1,000 to 50,000 and a lactone-modified hydroxyalkyl (meth) acrylate; and an unsaturated-group-containing polycarboxylic acid resin having an acid value of 40 to 160 mgKOH/g and obtained by reacting a phenol novolak type epoxy resin, a cresol novolak type epoxy resin and an unsaturated carboxylic acid in an acid equivalent/epoxy equivalent ratio of from 0.2 to 1.0 to prepare a reaction product and then reacting a hydroxyl group of the reaction product with a saturated or unsaturated polybasic acid anhydride in an acid equivalent/hydroxyl group equivalent ratio of 0.2 or higher.
However, as a permanent protective coating for a high-density printed wiring board, heat resistance and anti-migration properties become problems. Therefore, there is more preferably used an unsaturated-group-containing polycarboxylic resin (e) whose molecule contains a polyfunctional cyanate ester compound. A preferred resin is an unsaturated-group-containing polycarboxylic resin having an acid value of preferably 40 to 200 mgKOH/g, more preferably 50 to 160 mgKOH/g, and obtained by reacting 100 parts by weight of epoxy acrylate with 5 to 40 parts by weight of a polyfunctional cyanate ester compound to prepare a resin and then reacting the resin with 10 to 90 parts by weight of a polybasic acid anhydride. When the acid value is smaller than the above lower limit, undesirably, the solubility of an obtained photo-setting/thermosetting resin in an alkaline aqueous solution decreases. When the acid value is larger than the above lower limit, undesirably, the electric properties of cured coating of an obtained photo-setting/thermosetting resin decrease. The amount of the unsaturated-group-containing polycarboxylic resin is 20 to 90% by weight, preferably 25 to 70% by weight. When the amount of the unsaturated-group-containing polycarboxylic resin is smaller than the lower limit of the above range, undesirably, the photo-setting/thermosetting type resist is poor in photosensitivity. When it is larger than the above upper limit, undesirably, photo-setting/thermosetting type resist cures insufficiently in some cases.
In the unsaturated-group-containing polycarboxylic resin (e) whose molecule contains a polyfunctional cyanate ester compound, used in the present invention, an epoxy acrylate used as a raw material is a reaction product of an epoxy resin and an acrylic acid. Examples thereof includes a bisphenol A type epoxy acrylate, a bisphenol F type epoxy acrylate, a biphenol-epoxy acrylate, tetramethylbiphenol-epoxy acrylate, hexamethylbiphenol-epoxy acrylate and xylene novolakepoxy acrylate. These may be used alone or in combination.
The polybasic acid anhydride used in the acid modification reaction of component (e) of the present invention can be selected from generally known acid anhydrides having at least two carboxylic anhydrides per molecule. Specifically, it includes phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, naphthalene-1,4,5,8-tetracarboxylic acid dianhydride, benzophenontetracarboxylic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 4-methylhexahydrophthalic anhydride, 3-methylhexahydrophthalic anhydride, succinic anhydride, dodecenylsuccinic anhydride, and other substances having a molecule containing an acid anhydride. These anhydrides are used alone or in combination.
Although the conditions under which epoxy acrylate reacts with a polyfunctional cyanate ester compound are not specially limited, the amount of the polyfunctional cyanate ester compound per 100 parts by weight of the epoxy acrylate is generally 5 to 40 parts by weight, preferably 10 to 30 parts by weight. The reaction temperature is generally 50 to 100xc2x0 C. and the reaction period of time is generally 5 to 100 hours. A solvent may be used for controlling a viscosity during reaction. Although not specially limited, the solvent specifically includes ketons such as acetone, methyl ethyl ketone and methyl isobutyl ketone; acetates such as dipropylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monoethyl ether acetate and diethylene glycol monomethyl ether acetate; and aromatic hydrocarbons such as solvent naphtha, toluene and xylene. These solvents are used alone or in combination.
Next, the carboxylic acid modification of the above resin is carried out with the polybasic acid anhydride. In this modification, the above reaction product modified by reacting 100 parts by weight of epoxy acrylate with 5 to 40 parts by weight of a polyfunctional cyanate ester compound is reacted with 10 to 90 parts by weight of a polybasic acid anhydride. The thus-obtained resin has an acid value of 40 to 200 mgKOH/g, preferably 50 to 160 mgKOH/g. In this case also, a solvent may be added to control a viscosity. Specifically, the above solvents and esters such as propylene glycol monomethyl ether and dipropylene glycol monomethyl ether are used. The amount of the unsaturated-group-containing polycarboxylic resin (e) based on the photo-setting/thermosetting type resist resin composition is 20 to 90% by weight, preferably 25 to 70% by weight.
Next, the photopolymerizable compound having an ethylenic unsaturated double bond as component (f) used in the photo-setting type resist or the photo-setting/thermosetting type resist of the present invention includes (meth)acrylic acid esters of dihydric or higher alcohols. Examples of the dihydric or higher alcohols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, hexanediol, heptanediol, neopentyl glycol, 1,10-decanediol, cycloheptanediol, 1,4-cyclohexanedimethanol; polyethylene glycols such as diethylene glycol and triethylene glycol; polypropylene glycols such as dipropylene glycol and tripropylene glycol; xylenediol, 2-ethyl-1,3-hexanediol, biphenol, catechol, resorcinol, pyrogallol, glycerine, trimethylol ethane, trimethylol propane, pentaerithritol, dipentaerithritol, tripentaerithritol, sorbitol, glucose, butanetriol, 1,2,6-trihydroxyhexane and 1,2,4-benzenetriol.
Further, there may be used allyl compounds such as polyallyl esters of adipic acid, phthalic acid, terephthalic acid and trimellitic acid, polyallyl esters of polysulfonic acid, diallyl ether and triallylisocyanurate. Further, there maybe used polyvinyl compounds such as divinylbenzene, divinyl sulfone, divinyl phthalate and divinyl terephthalate. In addition, there may be used known compounds and resins. These compounds are used alone or in combination. The amount thereof is 1 to 30% by weight, preferably 2 to 20% by weight.
In order to photoinitiate a polymerization, a photopolymerization initiator (component g) is added to the photo-setting type resist or the photo-setting/thermosetting type resist used in the present invention. Examples of the photopolymerization initiator include xcex1-diketons such as benzyl and acetyl; acyloins such as benzoyl; acyloin ethers such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether and benzoin isobutyl ether; thioxanthones such as thioxanthone and 1,4-diethylthioxanthone; benzophenones such as benzophenone, 4,4xe2x80x2-bis(dimethylamino)benzophenone; acetophenones such as acetophenone, 1,2xe2x80x2-dimethoxy-2-phenylacetophenone and p-methoxy acetophenone; quinones such as anthraquinone and 1,4-naphthoquinone; and peroxides such as di-t-butylperoxide. These initiators are used alone or in combination. The amount thereof is 0.1 to 20% by weight, preferably 0.2 to 15% by weight.
When the epoxy compound, especially an alicyclic epoxy resin and/or an oxetane resin, is added, it is preferred to add a cationic phtotopolymerization initiator. Examples thereof includes known polymerization initiators such as an aromatic sulfonium salt and a complex of iron, e.g., xcex75-2,4-cyclopentadiene-1-yl)[(1,2,3,4,5,6-xcex7)-(1-ethylehtyl)bezene]-iron(1+)-hexafluorophosphate(1xe2x88x92). These polymerization initiators are used alone or in combination. The amount of the above polymerization initiator per 100 parts by weight of the epoxy compound is 0.1 to 10 parts by weight, preferably 0.2 to 5 parts by weight.
The thermosetting type resist is applied to a printed wiring board surface by a screen printing or the like and cured by heating alone to form a permanent protective coating. Generally known thermosetting type resists are used. Although not specially limited, the resin to be used includes generally known resins such as an epoxy resin, a polyfunctional cyanate ester resin, a maleimide resin and an unsaturated-group-containing polyphenylene ether resin. These resins are used alone or in combination as required.
The thermosetting type resist composition used in the present invention is cured itself under heat. Since, however, its curing rate is low in some cases, it is poor in workability, economic performances, etc. In such cases, a known heat-curing catalyst may be added into the thermosetting resin. The amount of the catalyst is 0.01 to 5% by weight, preferably 0.015 to 3% by weight. The resist composition in the present invention is used as a homogeneous solventless type by combining respective components or it is used as a solution obtained by dissolving or suspending a resin composition mainly formed of solid components in a solvent.
It is preferable that, before incorporation, the resin composition of the present invention is dissolved in a solvent in which it is soluble. The solvent in which the polyfunctional cyanate ester compound is soluble is not specially limited so long as it can dissolve the above compound. Examples thereof include ketons such as acetone, methyl ethyl ketone and methyl isobutyl ketone; esters such as ethyl acetate, isobutyl acetate, n-butyl acetate, ethylene glycol monoacetate, propylene glycol acetate and dipropylene glycol monoacetate; aromatic hydrocarbons such as toluene and xylene. These solvents are used alone or in combination. Preferably, for inhibiting the viscosity of the solution from increasing because of the evaporation of the solvent, a solvent which has a relatively high boiling point and is hard to evaporate at room temperature is used.
Further, the above solvents may be used to the unsaturated-group-containing polycarboxylic acid resin as component (e). Solvents other than the above solvents may be used and examples thereof include ethylene glycol alkyl ethers; diethylene glycol alkyl ethers; propylene glycol alkyl ethers; and dipropylene glycol alkyl ethers. These solvents are used alone or in combination.
As a method for imparting flame retardancy to these resist compositions, the present invention adopts a specific flame-retardant combination to attain self-extinguishing properties. That is, as flame-retardant components, 100 to 140 parts by weight of (a) aluminum hydroxide, 0.1 to 15 parts by weight of (b) a molybdenum compound and 0.1 to 10 parts by weight of (c) a zinc stannate type compound are incorporated into 100 parts by weight of the resin component, whereby self-extinguishing properties (flame resistance: UL 94 V-0) are attained.
The aluminum hydroxide as component (a) of the present invention may be selected from aluminum hydroxides produced by a known method. The aluminum hydroxide has an average particle diameter of 5 xcexcm or less, preferably 1 xcexcm or less. The aluminum hydroxide includes 3 crystallization water. The 3 crystallization water can be used by converting its value to approximately 2 to 2.5 as an average value by heating. When the crystallization water is heated too much and converted into 2 or lower crystallization water, undesirably, the heat-resistant effect decreases.
The molybdenum compound which is another flame-etardant component refers to a compound containing molybdenum. The molybdenum compound may be selected from generally known molybdenum compounds. Specific examples thereof include molybdenum oxide, molybdenum boride, molybdenum silicate, molybdenum sulfide, zinc molybdate, calcium molybdate and ammonium molybdate. These compounds as a powder may be dispersed, as it is, in the resist composition, while preferably the molybdenum compound is supported on an inorganic filler having an average particle diameter of 5 xcexcm or less such as talc, zinc oxide or calcium carbonate before use. As a production method for supporting the molybdenum compound on an inorganic filler carrier, for example, there may be used the method disclosed in U.S. Pat. No. 3,969,127. These molybdenum compounds may be used alone or in combination. 0.1 to 15 parts by weight, preferably 0.5 to 10 parts by weight, of the molybdenum compound together with 100 to 140 parts by weight of the aluminum hydroxide is used per 100 parts by weight of the resin.
The zinc stannate type compound which is further another flame retardant component is added in an amount of 0.1 to 10 parts by weight, thereby increasing the level of flame resistance (V-0). The zinc stannate type compound used in the present invention specifically includes zinc hydroxystannate and zinc stannate. These compounds may be used alone or in combination.
Of course, each of the above flame-retardants can be added in an amount larger than the above amounts. In this case, however, the resist composition itself undesirably becomes fragile or decreases in heat resistance when the resist composition is cured. When each of the above flame-retardants is added in an amount smaller than the above amounts, the flame resistance does not become V-0.
The resist composition of the present invention may contain various additives as desired so long as the inherent properties of the composition are not impaired. Examples of the additives include polyfunctional maleimides, polybutadiene, maleated butadiene, a butadiene-acrylonitrile copolymer, a butadiene-styrene copolymer, acrylic rubber, AS resin, ABS resin, MBS resin, unsaturated-group-containing PPE resin, polyphenylene ether, polysulfone, polyester, polyphenylene sulfide, polystyrene and polyurethane. Further, various known additives such as an organic filler, an inorganic filler, a dye, a pigment, other flame retardant, a thickener, a lubricant, an anti-foamer, a dispersing agent, a leveling agent, a photo-sensitizer and a thixotropic agent may be used alone or in combination as required. A curing agent or a catalyst is incorporated into a compound having a reactive group as required.
The pigment used for coloring is not specially limited. Generally, there may be used a known pigment which preferably has no halogen atom in a molecule. As a blue pigment, it includes copper phthalocyanine blue (C.I. Pigment Blue 15), nickel phthalocyanine blue, nonmetallic phthalocyanine blue (C.I. Pigment Blue 16), iron phthalocyanine blue, alkali blue (C.I. Pigment Blue 1, 2, 3, 10, 14, 18, 19, 24, 56, 57, 61), prussian blue (C.I. PigmentBlue 27), ultramarine (C.I. Pigment Blue 29), cobalt blue (C.I. Pigment Blue 28), sky blue (C.I. Pigment Blue 35) and cobalt phthalocyanine (C.I. Pigment Blue 75). These pigments have no halogen atom such as chlorine in a molecule. As an yellow pigment, there is preferably used enzimidron yellow (C.I. Pigment Yellow 120, 151, 175, 180, 181, 194), anthraquinone yellow (C.I. Pigment Yellow 123, 147), isoindolin yellow (C.I. Pigment Yellow 139, 185) and metal complex (C.I. Pigment Yellow 150, 153, 177, 179) each of which has no halogen atom in a molecule. Pigments having colors other than the above colors can be used. However, for preparing the intended halogen free resist composition of the present invention, a pigment whose molecule has no halogen atom is used rather than a conventional green pigment containing a halogen atom in a molecule. The above pigments whose molecule has no halogen atom may be used in combination.
The resist composition of the present invention can be applied to a printed wiring board by a generally known method such as a screen printing method, a roll coater method or a curtain coater method. The resist compositions of the present invention are cured by an optimal curing pattern for each of a thermosetting type, a UV-and-heat-combination type (photo-setting/thermosetting type) and a UV-setting type. For example, the thermosetting type resist is applied to a printed wiring board surface by screen printing, etc., a solvent is removed from the applied thermosetting type resist by drying under heat as required, and then the thermosetting resin is cured by heating. As for the photo-setting/thermosetting type resist, the photo-setting/thermosetting type resist is applied to a material to be covered, such as a printed wiring board, the applied photo-setting/thermosetting type resist is pre-dried to remove a solvent, necessary portions of the pre-dried photo-setting/thermosetting type resist are selectively photically cured by irradiation of an active energy ray such as ultraviolet ray, not-cured portions are developed and removed with a dilute alkaline aqueous solution, etc., and then a post-curing is carried out by heating. Thereafter, nickel plating and gold plating are carried out by electroless plating or electrolytic plating as required, to obtain a printed wiring board for mounting a semiconductor chip. As for the photo-setting type resist, the photo-setting type resist is applied to a material to be covered, the applied photo-setting type resist is dried to remove a solvent as required, and then the photo-setting type resist is cured by light.
After the application, a solvent is removed by pre-drying under heat as required. A generally known device such as a hot-air drying furnace may be used for the drying. In the case of the photo-setting/thermosetting type resist, for example, the drying temperature is 30 to 100xc2x0 C. preferably 50 to 80xc2x0 C. When the drying temperature is low, too long drying time is required and working efficiency is therefore poor. When the drying temperature is high, resin members are reacted with each other and therefore it becomes difficult to dissolve the resist with a developer. The drying time is 10 minutes to 2 hours, preferably 15 to 60 minutes.
The printed wiring board used in the present invention can be used by only polishing a patterned copper conductor surface before the application of the photo-setting/thermosetting type resist. However, it is preferred to roughen the copper surface and then treat the printed wiring board by a rustproofing treatment containing a copper chelate agent in advance. The rustproofing treatment improves adhesion between the copper conductor and the resin, which provides great improvements such as a decrease of an insulating-property deterioration after a pressure-cooker treatment or no occurrence of peelings.
The rustproofing agent may be selected from generally known rustproofing agents. Further, the copper chelate agent may be selected from generally known copper chelate agents. Examples of these include polybenzimidazole and chromate treatment. These agents are used alone or in combination. For example, there is preferably used a rustproofing solution, CL8300E, supplied by Meck K.K.
A coating of the photo-setting/thermosetting resin, applied on a printed wiring board, is covered with a film and exposed to irradiation of parallel light through the film, when the photo-setting/thermosetting resin is solventless. When it is a solvent type resin, the coating of the photo-setting/thermosetting resin is covered with a film after removing the solvent and then exposed to an active energy ray to photically cure necessary portions. Portions which are not exposed to light are dissolved and removed with a developer, then the photo-setting/thermosetting resin is post-cured by heating and nickel plating and gold plating are carried out to complete a printed wiring board.
As an irradiation light source of an active energy ray for curing the photo-setting type resist and the photo-setting/thermosetting type resist by light, there is used a low-pressure mercury lamp, a middle pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a xenon lamp or a metal halide lamp. Although the luminous exposure is not specially limited, it is generally 100 to 3,000 mJ/cm2, preferably 300 to 2,000 mJ/cm2. In addition to the above light sources, an electron ray and a laser can be used.
A coating of the photo-setting/thermosetting type resist is developed by a generally known method such as a spray developing method or a dip developing method in which a printed wiring board is dipped and shaken in a developer. The temperature of the developer is 5 to 50xc2x0 C. preferably 25 to 40xc2x0 C. When the temperature is low, the problem is that too long developing time is taken or that developing properties are poor. When the temperature is high, the cured portions which have been exposed to light are dissolved. The developer includes generally known dilute alkaline aqueous solution such as an aqueous solution of sodium carbonate, sodium hydroxide or ammonium hydroxide. Further, there may be also used an aqueous solution obtained by adding an water-soluble organic solvent into water and an aqueous solution obtained by adding an water-soluble organic solvent and an alkali agent into water. The amount of the alkali agent in the aqueous solution is preferably 0.1 to 5% by weight.
The water-soluble organic solvent includes generally known organic solvents such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, methyl lactate, ethyl lactate, butyl lactate, diethylene glycol, methanol, ethanol, propanol, xcex3-butyrolactone and methyl cellosolve. The water-soluble organic solvent is used in an amount of 10 to 80% by weight, preferably 15 to 50% by weight, based on the entire aqueous solution. Further, an alkali agent such as sodium hydroxide, sodium silicate or monomethanol amine may be added for increasing developing properties.
The photo-setting/thermosetting type resist is cured by heating after developing. Further, the thermosetting type resist is applied by a screen printing and the applied thermosetting type resist is pre-cured to remove the solvent and then cured by heating. The curing temperature is 100 to 250xc2x0 C., preferably 120 to 180xc2x0 C. Thereafter, nickel plating and gold plating are carried out.
According to the present invention, there is provided a flame retardant-containing resist composition capable of providing a halogen-free, phosphorus-free and antimony-free coating which is excellent in safety and which itself has self-extinguishing properties (UL94 V-0). According to the present invention, further, there is provided a flame retardant-containing resist composition whose coating, obtained by applying the resist composition to a halogen-free printed wiring board and drying it, has self-extinguishing properties (V-0) as a whole. When a resist composition which itself does not have self-extinguishing properties (UL94 HB) or a resist composition which itself has a slight self-extinguishing properties (UL94 V-1) is applied to the surface of a halogen-free printed wiring board (UL94 V-0), dried and then cured, the resultant printed wiring board can not attain UL94 V-0 as a whole and has a flame resistance problem. As for a halogen-free resist using only a color pigment containing no halogen atom in a molecule, this resist itself does not show self-extinguishing properties. When the above resist is applied to a halogen-free printed wiring board and the applied resist is cured, the thus-obtained printed wiring board merely shows HB. In contrast, the flame retardant resist composition of the present invention shows excellent self-extinguishing properties (UL 94V-0) so that it is apparent that the flame retardant resist composition of the present invention is very effective for electronic devices requiring flame resistance. Further, the flame retardant resist composition of the present invention has a molecule containing a polyfunctional cyanate ester compound so that there can be obtained a preferable permanent protective coating for a printed wiring board which permanent protective coating is excellent in heat resistance and anti-migration properties required for the reliability of a printed wiring board that is becoming denser and denser.